OCTOBER 19-20, 2012 - YMCA University of Science & Technology

Proceedings of the National Conference on
Trends and Advances in Mechanical Engineering,
YMCA University of Science & Technology, Faridabad, Haryana, Oct 19-20, 2012
slightly greater than thickness of plate (Ulysse, 2002). The welding parameters such as tool rotational speed,
welding speed, axial force, etc., and tool pin profile play a major role in deciding the weld quality.
Many attempts have been made on FSW on aluminium alloys. Balasubramanian (2008) investigated the
mechanical properties in FSW on aluminium alloy using rotating non-consumable tool. Results concluded that
the process parameter such as tool rotational speed, welding speed, axial force plays a major role in deciding the
weld quality. He studied the effect of tool pin profile and tool shoulder diameter on FSP zone formation in
AA6061 aluminium alloy. Five different tool pin profiles (straight cylindrical, tapered cylindrical, threaded
cylindrical, triangular and square) with three different shoulder diameters are used to fabricate the joints.
Cabibbo et al. (2007) studied the microstructure and mechanical properties of friction stir welded 6056-T6
aluminium alloy using polarized optical and transmission electron microscopy. The microstructure revealed
different grain morphologies in the thermo-mechanically affected zones. Tensile tests showed that yield and
ultimate strength slightly lower across the weld compared to the parent material as well as a reduction in ductility
of the weld region. Cavaliere et al., (2009) showed the effect of process parameters on the mechanical and micro
structural properties of dissimilar AA6082–AA2024 joints produced by friction stir welding. Zheng et al., (2008)
conducted a study on fracture of welded thin walled aluminium structures for train safety. The material
characterization for plasticity and fracture of each of the material zones within the weld is reported as a
combination of experimental and numerical studies. Cui et al., (2007) showed that a high carbon steel joint can
be successfully friction stir welded without any pre-or post-heat treatment. It was proved that friction stir
welding enables us to properly control the cooling rate and peak temperatures, which was impossible using
traditional welding. Minton and Mynors (2006) described a methodology for determining if a conventional
milling machine is capable of being used to undertake friction stir welding. The methodology was tested by
providing same thickness welds of 6.3 mm and 4.6 mm 6082-T6 aluminium sheets.
Scialpi et al. (2007) studied the effect of different shoulder geometries on the mechanical and micro-structural
properties of a friction stir welded joints. The three different tools differed from shoulders with scroll and fillet,
cavity and fillet, and only fillet were used. Nakata et al. (2006) showed that an improvement in the mechanical
properties due to the micro structural modification of an aluminium die casting alloy by multi-pass friction stir
processing (MP-FSP), which is a solid-state micro structural modification technique using a frictional heat and
stirring action. The hardness of the MP-FSP sample is about 20 Hv higher than that of the base metal. The effect
of the welding speed on the microstructure, local and overall mechanical properties of friction stir welded joints
of aluminium alloy 6005A-T6 has been investigated by Simar et al. (2008). The fine hardening precipitation
within the heat-affected zone has been characterized by differential scanning calorimetry (DSC) and transmission
electron microscopy (TEM).
Single pass friction stir welding is not able to provide better results in case of thick work material plates which is
mainly due to the difficulty in finding a suitable backing material. Obviously the thickness of plate that can be
joined by FSW can be increased by passing the tool along both sides of the butted plates in sequence. The use of
the sequential double pass weld can almost double the plate thickness that can be joined, thereby significantly
increasing the industrial utility of the FSW joining process for other materials like steels etc. Considering these
facts, the objective of the present study is to investigate the influence of tool shape on the tensile strength of AA
1100 in single and double sided friction stir welds.
2. Experimental Setup
The base material used in this study was aluminium alloy AA1100 plates having thickness of 5mm. The base
material tensile strength was 117.33 N/mm² with elongation of 14.6 %. FSW trials were carried out on a vertical
milling machine with square butt joint configuration. A pair of work pieces of dimension 200mm ×200mm ×5
mm were abutted and clamped rigidly on the backing plate for welding. The tool geometry with 18 mm diameter
flat shoulder with chamfered edge straight cylindrical (SC), threaded (TH), triangular (TR) and square (SQ) pin
profile with circumferential diameter 6mm were used to fabricate the joints.
The tool material was high carbon high chrome steel (HCHCR) which provides high cutting speed with long life
to the material. The tool material is available in 20 mm diameter rod. Straight cylindrical and threaded tool
geometries were processed on the lathe machine and central grinding machine according to the dimensions
specified. Triangular and square pin profiles were processed on the milling machine by indexing. It had the
maximum size of square pin profiles tool 4.2 mm obtained from circumferential diameter 6mm and for
triangular, it was 5.2 mm sides. It is worth noting that for the double pass weld, the plates were turned over about
an axis along the weld after the first pass was made, so that the two welding passes started at the same position
along the joint interface, and the advancing side of the second pass was over the retreating side of the first pass
weld. All of the welds were carried out along the rolling direction of the steel plate.
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